Design of mmWave Broadband Rotary Joint and 360° Beam-Steering Rotenna Based on Gap Waveguide Technology

This work presents the design and fabrication of a groove gap waveguide-based rotary joint and a rotenna (rotary antenna) with 360° mechanical beam steering for wideband millimeter-wave (mmWave) applications. The proposed rotary joint incorporates two WR-22 to groove gap waveguide transitions, connected back-to-back with an innovative transformer. A key advantage of gap waveguide technology is its ability to operate without physical contact between the rotary joint’s components, allowing the rotor to rotate freely near the stator with an air gap, while wave leakage is suppressed. By replacing common coaxial connectors with standard waveguide flanges and introducing a novel transformer between the rotor and stator, we have successfully developed a wideband rotary joint suitable for mmWaves. To demonstrate the practical applicability of this concept, we designed a rotenna with 360° mechanical beam steering. This design addresses the common limitations of electronically steerable antennas, such as limited steering range, gain degradation, and high cost and complexity. To validate the concept, the prototypes of the proposed rotary joint and rotenna were fabricated and measured. The measured and simulated results show good agreement. The rotary joint exhibits a 44.4% fractional bandwidth over the frequency range of 35–55 GHz with an insertion loss below 0.68 dB. Additionally, the engineered rotenna demonstrates a peak realized gain of 13 dBi with no scan loss over the full 360° steering range.